1. Brief Description of the Invention
The present invention relates to improved polyurethane thickeners, often referred to as rheological additives, used to provide viscosity control, flow, leveling and other rheological properties to clear and high gloss aqueous systems such as clear coats and clear coatings including textile coatings. The invention also includes a method of making such improved polyurethane thickeners, clear aqueous systems containing such thickeners and a method of thickening clear aqueous systems using such thickeners.
Coatings have been widely used to beautify and in addition to protect an underlying substrate. A growing new area of coatings are clear aqueous systems used for example as automotive clear coats. Clear aqueous systems must provide transparency and depth of field, as well as other optical properties, after application in addition to protecting the underlying surface. Clear aqueous systems include automotive clear coatings, wood lacquers, paints and other clear coatings, varnishes and textile coatings.
The invention hereof involves the synthesis of a new family of polyurethane rheological polymers especially suitable for clear systems by combining, through a reaction process, a defined set of chemicals to make such polyurethane polymers. These polymers provide both good flow and leveling and gloss retention to clear water-based systems. There has been a need for some time for a rheological additive for clear systems which imparts Theological properties including sag resistance and shear thinning, and which simultaneously does not adversely affect the clarity, transparency and gloss of such clear systems. The product of the instant invention results in a valuable Theological additive for a large variety of modern clear and transparent aqueous systems. Some companies in the past have used polyurethane thickeners in clear systems, but this use has generally resulted in some amount of haziness in the finished film.
The Paint and Coatings Dictionary, published by the Societies For Coatings Technology in 1978, defines a clear system or coating as a transparent protective and/or decorative film. Typical applications for such clear coatings include interior clear wood finishes, furniture polishes, water-based lacquers and automotive clearcoat finishes, and many other common commercial uses.
2. Description of the Prior Art